Over recent years there has been a significant increase in the number of miners in the Pilbara region of Western Australia, targeting channel iron deposits (CID) located in valleys, intersected by ephemeral creeks and below the groundwater table. The falling iron ore price has triggered a drive to reduce cost and maximise yield. Creek diversions provide an opportunity to maximise the utilisation of orebodies and extend the life-of-mine.
Creek diversions that are required during mining operations to access ore and provide flood protection have been historically constructed as uniform engineered channels, designed primarily for flow conveyance while minimising earthworks costs; however, the design of diversions becomes more complex when they are required to function in a similar way to the existing creek system during operations, and remain stable during more extreme events that would typically occur following mine closure, in accordance with current regulatory guidance.
The design specifications for closure are often more rigorous than the operational phase, and could incur significant additional cost to implement retrospectively if not planned and designed upfront.
The complexity of diversion design depends on site-specific factors such as: the size of the creek to be diverted; hydrology; corridor restrictions; geomorphology; hydrogeology; geology; environmental and heritage values; potential impacts and the risk to operations and environment.
The complex interactions of these factors must be well understood and hydraulic modelling undertaken to characterise the existing creek system, demonstrate the diversions, provide adequate flood protection during operations, and can function in a similar way to the existing system following mine closure.
This paper presents key design considerations for Pilbara creek diversions, operational and closure requirements, mine planning considerations, risks, cost saving opportunities, and the benefits of an integrated approach to design.